Particle filter of metal foil and process for producing a particle filter

ABSTRACT

A particle filter of metal foil has walls defining fluid flow channels with inlets and outlets. A first channel has an open entry cross section at a first end side extended partway into the first channel. A second channel has an open exit cross section substantially corresponding to the entry cross section. One of the walls of the first channel has filter passage perforations leading to the second channel. A closure in the first channel, opposite the entry cross section, toward a second end side, closes off the first channel to the fluid. A process for producing a particle filter from metal foil includes pulling the metal foil from an endless storage device. A joining element or strip is applied to the metal foil. The metal foil is shaped into subsequent channels. The metal foil is wound or stacked to form first and second channels in opposite directions. The first channel has an open entry cross section at the first end side extending partway into the first channel. The first channel has a closure opposite the entry cross section toward the second end side. Mutually bearing contact surfaces of the channels are joined, creating a wholly metal foil particle filter.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation of copending InternationalApplication No. PCT/EP00/04640, filed May 22, 2000, which designated theUnited States.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a particle filter of metal foilhaving mutually adjacent channels through which a fluid can flow. Eachchannel has at least one inlet and an outlet. The particle filter alsohas adjacent first and second channels. The first channel has an openentry cross section at a first end side of the particle filter. Theinvention also relates to a process for producing a particle filter.

[0004] European Patent 0 134 002 B1 has disclosed a diesel exhaustfilter made from woven wire cloth and a process for its production. Thediesel exhaust filter is constructed from layers which can be placed ontop of one another or shaped helically to form an assembly. A layerincludes a corrugated or folded screening cloth and a planar, continuousor perforated covering layer. Two end surfaces of the diesel exhaustfilter are constructed in such a way that a closed end-face section liesopposite an open end-face section and an end-face section is closed bypinching. The corrugated or folded layer is pressed onto the planarlayer in folds for that purpose.

SUMMARY OF THE INVENTION

[0005] It is accordingly an object of the invention to provide aparticle filter of metal foil and a process for producing a particlefilter, which overcome the hereinafore-mentioned disadvantages of theheretofore-known products and processes of this general type and whichallow simplified production of the particle filter while at the sametime producing a large surface area in the particle filter.

[0006] With the foregoing and other objects in view there is provided,in accordance with the invention, a particle filter, comprising firstand second end sides. A metal foil forms walls defining mutuallyadjacent channels through which a fluid can flow. Each of the channelshas at least one inlet and at least one outlet. The channels includefirst and second adjacent channels defined by the walls formed of themetal foil. The first channel has an open entry cross section at thefirst end side extended at least partway into the first channel. Thesecond channel has an open exit cross section at least substantiallycorresponding to the entry cross section. At least one of the wallsdefining the first channel has perforations formed therein as filterpassages leading to the second channel. A closure is disposed at thefirst channel, opposite the entry cross section and toward the secondend side, for closing off the first channel to the fluid, at least asfar as possible.

[0007] The fact that the walls of the first and second channels are madefrom metal foil means that they each have a large surface area whichcomes into contact with the fluid. While only the individual filamentsof the cloth are available as surface area when using a woven wirecloth, a wall which helps to form the first channel has a surface thatis continuous apart from the perforations. The perforations, acting asfilter passages leading to the adjacent second channel, also have asurface with which the fluid can come into contact. Therefore, comparedto a woven wire cloth, a perforated wall of that type has a largersurface area which also has a larger active surface area, for example,either when provided with a suitable coating or when the material of themetal foil is selected appropriately. It can be utilized for catalyticor other reactions or possible applications of a particle filter of thattype.

[0008] The advantage of a large surface area is combined with theadvantage that such a particle filter can be produced in a small numberof working steps. The perforations which are required are, for example,prefabricated in the metal foil. The corresponding shaping to form theindividual channels is advantageously completed in a single workingstep, irrespective of whether or not the metal foil has perforations. Byway of example, it is advantageous if all of the walls which form thechannels have perforations, so that during production the metal foil orfoils can be processed independently of position and orientation.

[0009] Furthermore, perforating metal foil enables an accurate positionof the filter passages to be achieved in the subsequent particle filter.While woven wire cloth is at risk of filaments shifting duringprocessing, that is impossible in the case of perforations in the metalfoil. That type of filter passages also enables the density ofperforations to be varied over the metal foil and therefore the channelwall which is to be formed. It also enables a diameter of such aperforation to be varied. That option can be employed in particular ifdifferent filter stages are to be formed in the particle filter.

[0010] In order to avoid a high pressure loss across the particlefilter, the second channel has an open exit cross section whichcorresponds to the entry cross section. As a result, it is possible forthe pressure loss to be set approximately proportionally to the numberand dimensions of the perforations. In accordance with another featureof the invention, the closure of the first channel of the particlefilter is constructed in such a way that it does not allow any fluid topass through. In this case, the filter passages form the only entry tothe second channel. The closure of the first channel serves as a barrierwall, so that the fluid is forced through the filter passages. Particlescontained in the flow of fluid which accumulate at the filter passagesare then collected in the region of the closure. This can be assisted,for example, by providing a type of cage in the region of the closure.Due to the formation of the flow in the region of the closure, it ispossible for a dammed region of the fluid formed at that location to beutilized in such a way that although particles do reach that region,they are then deposited in that region. Consequently, the filterpassages remain clear and the particle filter requires fewerregeneration cycles. The particle filter may have suitable regenerationmeasures for regeneration such as, for example electrical heating, acatalytic coating or the like, in the region of the closure.

[0011] In accordance with a further feature of the invention, in orderto simplify production of the particle filter, the first channel and thesecond channel have the same structure but are disposed in oppositedirections relative to one another. This means that only one productiontool is required for a metal foil. In the case of a particle filterhaving a layered structure, all of the metal foils can initially passthrough production in one direction, and are only subsequently turned sothat they alternate in opposite directions relative to one another.Advantageously, the first and second channels also form a honeycomb bodywhich can preferably be produced in this way, with first and secondchannels alternating.

[0012] In accordance with an added feature of the invention, the wallsof the first and second channels are formed from a single metal foil.This enables the metal foil to be unwound from a roll of metal foil,then subjected to a desired perforation step and for a desired shape tobe imposed on the metal foil in the processing station which follows.The metal foil can then be formed into the particle filter either inwound or layered form. It is only at this working step that it isnecessary for the metal foil to be cut off the roll of metal foil. Theparticle filter which has been layered or wound in this manner has joinsthat are produced, for example, by brazing, at locations where theindividual walls touch one another.

[0013] In accordance with an additional feature of the invention, it ispreferable to use a metal foil which has a coating before it isprocessed. This coating may either be of a catalytic nature, with theresult that the surface of the particle filter is once again increasedin size considerably due to the coating, or the coating may also includea joining element, such as, for example, brazing material, for joiningwalls of the particle filter which are in contact with one another. Forthis purpose, by way of example, the joining element is applied to themetal foil in strip form during or before the processing to form theparticle filter. The joining element can also be applied, for example,to a suitable coating of the metal foil.

[0014] In accordance with yet another feature of the invention, in orderto increase the surface area of the particle filter, it has also provenadvantageous if the first and/or second channel has a tapering crosssection. This cross section is preferably in the shape of a wedge. Inthe case of the first channel, the tapering cross section serves as aninlet and, as a result, reduces the pressure loss of the fluid flowingin. Furthermore, the active surface area which is acted upon by fluid isincreased in size, since the fluid flows onto the surface at an angle.At the same time, this configuration enables particles which haveaccumulated at a filter passage to be, as it were, washed off by thefluid flowing onto the particles. As a result, the particles which areto be filtered out are moved onward into the region of the closure ofthe first channel. This movement of the particles is assisted by thefact that opposite walls of the metal filter in each case haveperforations. As a result, a laminar flow is formed along these walls,with the fluid remaining in motion along this laminar flow. Due toturbulence formed in the central region of a channel of this type, theparticles are carried onward, over the length of the channel, into theregion of the channel closure, where they can be deposited.

[0015] A further important parameter of a particle filter is thepressure loss which it causes. However, to enable a large surface areato be formed in combination with a high filter action but without a highpressure loss, tests have shown that it is expedient to adapt thediameter of the filter passages. Therefore, in accordance with yet afurther feature of the invention, the filter passage is a hole in themetal foil with a size of between 3 and 25 μm, preferably 5 μm. It ispossible to optimize these otherwise contradictory parameters with adiameter of this type. This is assisted if the particle filter hasapproximately between 80,000 and 120,000 filter passages per m² of wall.In this case, the square meter of wall is defined in such a way that theflowing fluid can flow onto it. Since the particle filter, particularlywhen used in motor vehicles, is exposed to high temperatures, it isnecessary for it to be thermally stable and also stable with respect tomechanical vibrations. In accordance with yet an added feature of theinvention, this can be achieved with a metal foil which makes itpossible to produce a wall with filter passages having a wall thicknessbetween 20 μm and 65 μm, preferably between 30 μm and 40 μm.Particularly if the wall is between 30 μm and 40 μm, it is possible toproduce the channels without major outlay when producing a particularlylightweight particle filter which, nevertheless, has sufficientstability and strength during operation.

[0016] In accordance with yet an additional feature of the invention,the coating of the particle filter is applied after the channels havebeen produced.

[0017] With the objects of the invention in view, there is also provideda process for producing a particle filter, especially the particlefilter described above, from metal foil, which comprises pulling themetal foil out of at least one endless storage device, applying ajoining element, in particular in strip form, to the metal foil, shapingthe metal foil for producing subsequent channels and winding or stackingthe metal foil to form first channels and second channels oriented inopposite directions. The first channel has an open entry cross sectiondisposed at a first end side of the particle filter and extending atleast partway into the first channel. The first channel also has aclosure disposed opposite the entry cross section toward a second endside of the particle filter. Contact surfaces of the channels bearingagainst one another are permanently joined, to create the particlefilter exclusively from metal foil.

[0018] In accordance with another mode of the invention, the metal foilis coated before or after the above steps.

[0019] In accordance with a concomitant mode of the invention, the metalfoil is perforated before or after the above steps.

[0020] Other features which are considered as characteristic for theinvention are set forth in the appended claims.

[0021] Although the invention is illustrated and described herein asembodied in a particle filter of metal foil and a process for producinga particle filter, it is nevertheless not intended to be limited to thedetails shown, since various modifications and structural changes may bemade therein without departing from the spirit of the invention andwithin the scope and range of equivalents of the claims.

[0022] The construction and method of operation of the invention,however, together with additional objects and advantages thereof will bebest understood from the following description of specific embodimentswhen read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a diagrammatic, elevational view of a first particlefilter made from metal foil which is coated;

[0024]FIG. 2 is a view similar to FIG. 1 of a second particle filterwhich is made from a metal foil;

[0025]FIG. 3 is a plan view showing a variation of perforation in ametal foil of a particle filter; and

[0026]FIG. 4 is a side-elevational view of a production line forproduction of a particle filter from metal foil.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Referring now to the figures of the drawings in detail and first,particularly, to FIG. 1 thereof, there is seen a first particle filter 1which has a first channel 2, a second channel 3 and a third channel 4.The first particle filter 1 is constructed from metal foils 5 which arelayered on top of one another. The metal foils 5 form walls 6 of thechannels 2, 3, 4. A first wall 7 and a second wall 8, which togetherform the first channel 2, have first perforations 9 as filter passagesleading to the second channel 3 and the third channel 4. A fluid 10which flows through the particle filter 1, as indicated by arrows,enters an open entry cross section 11 at a first end side 12 of theparticle filter 1. The entry cross section 11 extends into the firstchannel 2. The fact that the first channel 2 has a closure 13 oppositethe entry cross section 11, toward a second end side 14, means that thefluid is forced through the perforations 9. This is because acounterpressure, which forces the fluid 10 into the second channel 3 andthe third channel 4, is built up at the closure 13.

[0028] According to the illustrated embodiment, the closure 13 does nothave any perforations and is therefore closed off in a gastight mannerto the fluid 10 which can flow through. In another non-illustratedstructure, the closure 13 also has perforations. This allows the fluid10 to be guided through the entire length of the first channel 2.According to a further advantageous configuration, perforations areprovided only in a first region A of the closure 13, while there are noperforations in a second region B of the closure 13. As a result, thesecond region B acts as a dead space and a location for particles toaccumulate in the first channel 2, due to the lack of flow in thatregion.

[0029] The second channel 3 has an open exit cross section 15, whichcorresponds to the open entry cross section 11 of the first channel 2.The open entry cross section 11 and the open exit cross section 15illustrated in this figure have the advantage of acting as nozzles ordiffusers for the fluid 10, due to their narrowing or increasing insize. This contributes to minimizing pressure losses across the firstparticle filter 1. However, on one hand, it is also possible for theexit cross section 15 to be larger than the entry cross section 11, withthe result that the flow of fluid is slowed down. If, on the other hand,it is desired for the flow velocity to be increased downstream of theparticle filter, the exit cross section 15 may also be made smaller thanthe entry cross section 11.

[0030]FIG. 2 shows a second particle filter 16. The second particlefilter 16 is produced from a metal foil 17. A particle-laden secondfluid 18, indicated by an arrow, flows through a fourth channel 19 andthrough second perforations 20, into a fifth channel 21. The metal foil17 is folded in such a way that it forms third walls 22 of the channels19, 21 and second closures 23. The cross section of the channels 19, 21tapers. In a preferred configuration, the cross sections narrow in theshape of a wedge. In this way, it is possible to achieve a nozzle-likeeffect over the entire length of a channel and to increase the area ofeach channel onto which fluid flows.

[0031]FIG. 3 shows a part 24 of a metal foil with a variation of thirdperforations 25. A density of filter passages 26 increases over thelength of the part 24. This can be achieved by changing distancesbetween the filter passages 26, as well as the number and diameter ofthese passages. As illustrated, a fluid, indicated by an arrow,advantageously flows onto the part 24. The result is a flow in thechannel which uses the entire length of the part 24.

[0032]FIG. 4 shows an advantageous production line 27 which can be usedto carry out a process for producing a particle filter from metal foil,in particular a particle filter according to the present invention. Forthis purpose, a metal foil 29 is unwound from an endless storage device,in this case a roll of metal foil 28. In the next working step, ajoining element 30 is applied to the metal foil 29. This advantageouslytakes place in strip form, expediently along those regions in whichsurfaces that subsequently rest on top of one another are in contactwith one another and are to be joined to one another. In a further step,the subsequent channels of a particle filter are shaped. In theillustrated embodiment, this is carried out through the use of a firstpress 31 and a second press 32. The first press 31 stamps the samegeometry into the metal foil 28 as the second press 32. However, theyare rotated through 180° with respect to one another. During asubsequent working step, the stamped geometries 33 are separated fromthe metal foil 29, as is indicated by a knife blade and a double arrow.The stamping which is offset alternately through 180° allows thegeometries that have been stamped in this manner to be stackedcontinuously on top of one another. The stamping leads to first andsecond channels being formed, which on one hand have the same shape buton the other hand are disposed in opposite directions relative to oneanother. Then, in a working step which is not illustrated, contactsurfaces that bear against one another are permanently joined to oneanother, for example through the use of brazing, so that a particlefilter is formed purely from a metal foil. In the next working step ofthe production line 27, a particle filter 35 is perforated through theuse of a laser 34. The particle filter 35 is preferably provided, forexample, with a catalytic coating before the perforation is made, a stepwhich in turn increases the surface area of the particle filter 35.

I claim:
 1. A particle filter, comprising: first and second end sides; ametal foil forming walls defining mutually adjacent channels throughwhich a fluid can flow, each of said channels having at least one inletand at least one outlet; said channels including first and secondadjacent channels, said first channel having an open entry cross sectionat said first end side extended at least partway into said firstchannel, and said second channel having an open exit cross section atleast substantially corresponding to said entry cross section; at leastone of said walls defining said first channel having perforations formedtherein as filter passages leading to said second channel; and a closuredisposed at said first channel, opposite said entry cross section andtoward said second end side, said closure substantially closing off saidfirst channel to the fluid.
 2. The particle filter according to claim 1,wherein said filter passages form the only entry to said second channel.3. The particle filter according to claim 1, wherein said first andsecond channels have the same shape but open in mutually oppositedirections.
 4. The particle filter according to claim 1, wherein saidfirst and second channels alternate with one another to form a honeycombbody.
 5. The particle filter according to claim 1, wherein said wallsdefining said first and second channels are formed from a single metalfoil.
 6. The particle filter according to claim 1, wherein at least oneof said channels has a tapering cross section.
 7. The particle filteraccording to claim 6, wherein said tapering cross section iswedge-shaped.
 8. The particle filter according to claim 1, wherein saidfilter passages are holes in said metal foil having a diameter ofbetween 3 and 25 micrometers.
 9. The particle filter according to claim8, wherein said diameter is 5 micrometers.
 10. The particle filteraccording to claim 1, wherein said filter passages number substantiallybetween 80,000 and 120,000 per square meter of said walls.
 11. Theparticle filter according to claim 1, wherein one of said walls havingsaid filter passages is between 20 and 65 micrometers thick.
 12. Theparticle filter according to claim 11, wherein said one of said wallshaving said filter passages is between 30 and 40 micrometers thick. 13.The particle filter according to claim 1, including a coating on saidmetal foil.
 14. The particle filter according to claim 13, wherein saidcoating is applied after said channels have been produced.
 15. Theparticle filter according to claim 1, wherein said perforations areformed after said channels have been produced.
 16. A process forproducing a particle filter from metal foil, which comprises thefollowing steps: pulling the metal foil out of at least one endlessstorage device; applying a joining element to the metal foil; shapingthe metal foil for producing subsequent channels; winding or stackingthe metal foil to form first channels and second channels oriented inopposite directions; providing the first channel with an open entrycross section disposed at a first end side of the particle filter andextending at least partway into the first channel; providing the firstchannel with a closure disposed opposite the entry cross section towarda second end side of the particle filter; and permanently joiningcontact surfaces of the channels bearing against one another, to createthe particle filter exclusively from metal foil.
 17. The processaccording to claim 16, which further comprises applying the joiningelement to the metal foil in strip form.
 18. The process according toclaim 16, which further comprises coating the metal foil before the stepof pulling the metal foil out of the at least one endless storagedevice.
 19. The process according to claim 16, which further comprisescoating the metal foil after the step of permanently joining the contactsurfaces of the channels.
 20. The process according to claim 16, whichfurther comprises perforating the metal foil before the step of pullingthe metal foil out of the at least one endless storage device.
 21. Theprocess according to claim 16, which further comprises perforating themetal foil after the step of permanently joining the contact surfaces ofthe channels.
 22. The process according to claim 18, which furthercomprises perforating the metal foil before the step of coating themetal foil.
 23. The process according to claim 19, which furthercomprises perforating the metal foil after the step of coating the metalfoil.